Harvesting Aqua

Filtering And Treating Rainwater For Drinking

There are lots of uses for the rainwater that you have collected but to use as your drinking water is one of the highest effort though the most rewarding. Though rainwater is inherently drinkable, it picks up contaminants in the process of collection. From your roof, in the pipeline, or by developing algae if the water stagnates in your storage tank.

If you plan on drinking your collected rainwater, you’re going to need to filter and treat it. Otherwise, you risk ingesting a wide variety of waterborne illnesses, some of which could be very serious. If you want pure, safe, and free drinking water you’ll need to both filter and disinfect your water.


Filtration is a critical step, especially for rainwater harvesting. Filtrations’ purpose is to remove debris and particles and, as rainwater is often collected from a roof or surface, debris will be a persistent issue.

The first step is pre-tank filtration. Much of the debris that you will deal with from your roof will be large such as leaves and moss. It’s easiest to manage these larger pieces by preventing them from getting into your cistern or storage tank in the first place. Fortunately, there are a number of methods to do this, many of which are pretty cost-effective.

  • Gutter guards and strainers. These are cages, foam, or solid overhangs that sit over the top of your gutter and prevent debris from getting into the gutter but allow water.
  • Downspout filters. Rather than capturing the leaves and moss etc in your gutters, these are in your downspout and capture everything that your gutters funnel to them. 
  • First-flush diverters. This diverts the initial deluge of a storm or downpour away from your tank. The idea here is that the first “flush” of a storm brushes off most of the debris and after that, you get mostly debris-less water

Ultimately, whether you plan on drinking your rainwater or not, pre-tank filtration is a good idea. For a relatively low cost, you can prevent some major headaches by keeping leaves and moss out of your tank.

Viruses are generally .004 to 0.1 microns large

Some additional filtration is highly recommended though if you do plan on drinking your rainwater. While the pre-tank filtration can prevent a lot of the larger debris, there are always smaller, and even microscopic particles that you are definitely going to want to filter. In fact, in a lot of places, there may even be laws for how filtered your water must be in order to drink it. It’s worth looking into what your local regulations are before you get started in setting up a drinking water harvesting system.

What most drinking systems have is an inline filtration system with two sediment filters. They’re called inline as the filters aren’t in the tank but they are in the output lines where the water is pumped out of the tank. In most cases, there are two filters whose effectiveness is measured in microns. The first is a 20-10 micron filter and the second is generally a 10-5 micron filter.


This amount of filtration is generally good for just about all types of sediment but many of the bacteria and viruses for the most common waterborne illnesses are smaller than this and they’re simply difficult to filter out. This is why it’s necessary to disinfect the water as well in order to make it truly safe to drink.

When it comes to disinfection you have a few options that come with their own pros and cons.

  • Chemical. The most common method of chemical disinfection is to use Chlorine or Iodine. The challenges here are that Chlorine can leave some toxic chemical by-products and Iodine can leave an unpleasant taste (and my be unhealthy for pregnant women or people with thyroid problems
  • UV Lights. Likely the most expensive option, UV disinfection is a low maintenance choice that is the most effective choice. It’s biggest drawback is that the water must be mostly clear as the shadows from particles can allow infectants to survive but if you’ve filtered your water using the methods above, this shouldn’t be an issue.
  • Boiling. There’s always the good old stand-by of boiling the water. Though it’s effective, this option requires so much energy to pull-off that doing so at scale can make it a difficult option to manage.

The above are the most common options but lately there have been some astounding advances in distillation technology. This is to say there are other option but less is known about them and, at this point, they may not be quite as cost-effective.

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